There are many technological applications that require that two or more components be rigidly positioned with respect to each other. A single example will suffice to illustrate this point. Many, if not most, optical communications systems inject light from a semiconductor laser into an optical fiber. The light emitted from the laser is concentrated in a very narrow angular region or cone. Optical communications systems typically transmit information more accurately with higher optical power, and the efficiency with which light from the laser is injected into the fiber is a critical system parameter. High injection efficiency between the laser and the fiber depends upon the laser and the optical fiber being accurately aligned with respect to each other. For example, in a typical present day laser package, a 1 .mu.m misalignment of the laser with respect to the fiber can result in a 3 dB loss of light coupled into the fiber. The alignment must not only be initially accurate but must also be rigid and not susceptible to change while the laser is used under varying conditions.
As might be anticipated, many methods that align optical fibers and lasers with respect to each other have been investigated for use in making optical packages. The simplest techniques use epoxy or solder to maintain the relative position of the fiber and laser. These techniques, however, do not provide great rigidity as the package is used and subjected to varying ambient conditions. Relative alignment of the laser and fiber can vary during use. A technique that can provide greater precision and durability is laser welding. Advantages of this technique include: 1) joint strength that approaches that of the parent materials; 2) minimal contamination because the process is fluxless and does not require a filler material; and 3) localized heating that confines distortion effects to a relatively small area around the weld zone. Laser welding is well known. See, for example, U.S. Pat. No. 5,218,258, issued on Jun. 8, 1993 to Shirasu et al.
However, the successful implementation of laser welding is not without problems. The localized heating produced in laser welding creates thermoelastic deformations and stresses in the welded components. The thermal distortions that result cause small relative movements between the laser and the optical fiber which can significantly degrade the amount of light coupled into the optical fiber. Even clamping of the components does not completely eliminate the small or micro movements of the components.
Real time monitoring and correction of the relative positions during the welding process would be desirable. Such monitoring and correction has been provided in diamond turning to correct geometrical errors, that is, adjust position, and in lithography to provide high resolution positioning by many types of actuators including piezoelectric, dc or stepping motors, linear drives. These actuators provide high resolution positioning in small time intervals. Since weld time intervals are small, fast response time positioners are required. However, use of piezoelectric actuators for relative position control during a joining process has not been extended to optical packages.
The use of piezoelectrics in optical packages is known. See, for example, U.S. Pat. No. 5,058,124 issued on Oct. 15, 1991 to Camerson et al. (Camerson). Camerson describes the use of a piezoelectric stack to position an external cavity with respect to a laser chip.